[web] revise flag ort.env.wasm.simd (microsoft#24314)

### Description

This PR revised the flag `ort.env.wasm.simd` to enhance its usage so
that more use scenarios are covered.
- Allow setting to `false` explicitly to disable SIMD checking. resolves
microsoft#24292 (@Eldow)
- Allow setting to `'relaxed'` to enable Relaxed SIMD checking. Relaxed
SIMD is introduced first in microsoft#22794 (@jing-bao)
- Behavior is not changed when not setting (ie. `undefined`) or setting
to `true`
- Added a warning message when setting to unknown value, and reset to
`false` in this case

Author: fs-eire

js/common/lib/env.ts

@@ -41,16 +41,22 @@ export declare namespace Env {
     numThreads?: number;
 
     /**
-     * set or get a boolean value indicating whether to enable SIMD. If set to false, SIMD will be forcely disabled.
+     * set a value indicating whether to enable SIMD.
+     *
+     * ONNX Runtime will perform feature detection based on the value of this property. Specifically, when the value is
+     * set to:
+     * - `undefined`, `true` or `"fixed"`: will check availability of Fixed-width SIMD.
+     * - `"relaxed"`: will check availability of Relaxed SIMD.
+     * - `false`: will not perform SIMD feature checking.
+     *
+     * Setting this property does not make ONNX Runtime to switch to the corresponding runtime automatically. User need
+     * to set `wasmPaths` or `wasmBinary` property to load the corresponding runtime.
      *
      * This setting is available only when WebAssembly SIMD feature is available in current context.
      *
      * @defaultValue `true`
-     *
-     * @deprecated This property is deprecated. Since SIMD is supported by all major JavaScript engines, non-SIMD
-     * build is no longer provided. This property will be removed in future release.
      */
-    simd?: boolean;
+    simd?: boolean | 'fixed' | 'relaxed';
 
     /**
      * set or get a boolean value indicating whether to enable trace.

js/web/lib/backend-wasm.ts

@@ -17,12 +17,13 @@ export const initializeFlags = (): void => {
     env.wasm.initTimeout = 0;
   }
 
-  if (env.wasm.simd === false) {
+  const simd = env.wasm.simd;
+  if (typeof simd !== 'boolean' && simd !== undefined && simd !== 'fixed' && simd !== 'relaxed') {
     // eslint-disable-next-line no-console
     console.warn(
-      'Deprecated property "env.wasm.simd" is set to false. ' +
-        'non-SIMD build is no longer provided, and this setting will be ignored.',
+      `Property "env.wasm.simd" is set to unknown value "${simd}". Reset it to \`false\` and ignore SIMD feature checking.`,
     );
+    env.wasm.simd = false;
   }
 
   if (typeof env.wasm.proxy !== 'boolean') {

js/web/lib/wasm/wasm-factory.ts

@@ -64,6 +64,34 @@ const isSimdSupported = (): boolean => {
   }
 };
 
+const isRelaxedSimdSupported = (): boolean => {
+  try {
+    // Test for WebAssembly Relaxed SIMD capability (for both browsers and Node.js)
+    // This typed array is a WebAssembly program containing Relaxed SIMD instructions.
+
+    // The binary data is generated from the following code by wat2wasm:
+    // (module
+    //   (func (result v128)
+    //      i32.const 1
+    //      i8x16.splat
+    //      i32.const 2
+    //      i8x16.splat
+    //      i32.const 3
+    //      i8x16.splat
+    //      i32x4.relaxed_dot_i8x16_i7x16_add_s
+    //   )
+    //  )
+    return WebAssembly.validate(
+      new Uint8Array([
+        0, 97, 115, 109, 1, 0, 0, 0, 1, 5, 1, 96, 0, 1, 123, 3, 2, 1, 0, 10, 19, 1, 17, 0, 65, 1, 253, 15, 65, 2, 253,
+        15, 65, 3, 253, 15, 253, 147, 2, 11,
+      ]),
+    );
+  } catch (e) {
+    return false;
+  }
+};
+
 export const initializeWebAssembly = async (flags: Env.WebAssemblyFlags): Promise<void> => {
   if (initialized) {
     return Promise.resolve();
@@ -82,7 +110,14 @@ export const initializeWebAssembly = async (flags: Env.WebAssemblyFlags): Promis
   let numThreads = flags.numThreads!;
 
   // ensure SIMD is supported
-  if (!isSimdSupported()) {
+  if (flags.simd === false) {
+    // skip SIMD feature checking as it is disabled explicitly by user
+  } else if (flags.simd === 'relaxed') {
+    // check if relaxed SIMD is supported
+    if (!isRelaxedSimdSupported()) {
+      throw new Error('Relaxed WebAssembly SIMD is not supported in the current environment.');
+    }
+  } else if (!isSimdSupported()) {
     throw new Error('WebAssembly SIMD is not supported in the current environment.');
   }